Atmospheric Chemistry of HOHgO Mimics That of a Hydroxyl Radical.

HOHgO, formed from HOHg + O, is a key intermediate in the OH-initiated oxidation of Hg in the atmosphere. As no experimental data are available for HOHgO, we use computational chemistry (CCSD(T)//M06-2X/AVTZ) to characterize its reactions with atmospheric trace gases (NO, NO, CH, CH, CHO and CO). In summary, HOHgO, like the analogous BrHgO radical, largely mimics the reactivity of OH in reactions with NO, alkanes, alkenes, and aldehydes. The rate constant for its reaction with methane (HOHgO + CH → Hg(OH) + CH) is about four times higher than that of •OH at 298 K. All of these reactions maintain mercury as Hg, except for HOHgO + CO → HOHg + CO. Considering only the six reactions studied here, we find that reduction by CO dominates the fate of HOHgO (79-93%) in many air masses (in the stratosphere and at ground level in rural, marine, and polluted urban regions) with only modest competition from HOHgO + CH (<15%). We expect that this work will help global modeling of atmospheric mercury chemistry.